The present invention relates to seals in a gas turbine for supplementing the chordal hinge seals between turbine nozzles and a turbine nozzle support ring and particularly relates to supplementary seals for substantially minimizing or eliminating leakage losses past the chordal hinge seals.
In a gas turbine, hot gases of combustion flow from combustors through first-stage nozzles and buckets and through the nozzles and buckets of follow-on turbine stages. The first-stage nozzles typically include an annular array or assemblage of cast nozzle segments each containing one or more nozzle stator vanes per segment. Each first-stage nozzle segment also includes inner and outer band portions spaced radially from one another. Upon assembly of the nozzle segments, the stator vanes are circumferentially spaced from one another to form an annular array thereof between annular inner and outer bands. A nozzle retaining ring coupled to the outer band of the first-stage nozzles supports the first-stage nozzles in the gas flow path of the turbine. An annular nozzle support ring, preferably split at a horizontal midline, is engaged by the inner band and supports the first-stage nozzles against axial movement.
In an exemplary arrangement, eighteen cast segments are provided with two vanes per segment. The annular array of segments are sealed one to the other along adjoining circumferential edges by side seals. The side seals seal between a high pressure region radially inwardly of the inner band, i.e., compressor discharge air at high pressure, and the hot gases of combustion in the hot gas flow path which are at a lower pressure.
Chordal hinge seals are used to seal between the inner band of the first-stage nozzles and an axially facing surface of the nozzle support ring. Each chordal hinge seal includes an axial projection which extends linearly along a chord line of the inner band portion of each nozzle segment. Particularly, the chordal hinge seal extends along an inner rail of each segment and which rail extends radially inwardly of the inner band portion. The chordal hinge seal projection lies in sealing engagement with the axially opposite facing sealing surface of the nozzle support ring.
During operation and/or repair of the first-stage nozzle, it has been found that warpage can leave gaps between the chordal hinge seals and the sealing surface of the nozzle support ring. These gaps enable leakage past the chordal hinge seals from the high pressure area radially within the annular inner band into the hot gas flow path. That is, the chordal hinge seals are inadequate to prevent leakage flow as the chordal hinge seal projections lose contact with the sealing surface of the nozzle support ring. Consequently, there is a need for a supplemental seal at the interface of the first-stage nozzles and nozzle support ring to minimize or eliminate the leakage flow past the chordal hinge seals.
In accordance with a preferred embodiment of the present invention, there is provided a supplemental seal between the first-stage nozzles and the nozzle support ring which eliminates or minimizes leakage past the chordal hinge seals and which is readily and easily installed without reconfiguration of the first-stage nozzles or nozzle support ring. In a first embodiment hereof, segmented sheet metal supplemental seals are disposed in an annular cavity defined between radially inwardly and outwardly facing surfaces of the inner band of the nozzle segments and the nozzle support ring, respectively. The cavity is also defined by an annular axial facing surface of the first-stage nozzles, i.e., an annular surface along the radially inwardly extending inner rails of the inner band.
The supplemental seal, in this first embodiment, includes a plurality of arcuate sheet metal seal sections each having a generally U-shape in circumferential cross-section and a radially inwardly extending first anchor leg or support portion. This first anchor leg is disposed between the annular facing surfaces of the nozzle support ring and the inner rails at a location radially outwardly of the chordal hinge seals. The second and third portions, i.e., the legs of the U-shaped seal, bear against the radial inner and outer surfaces of the inner band and nozzle support ring, respectively. The base of the U-shaped section is spaced from the axial surface of the inner rail. Should leakage air flow past the first portion of the supplemental seal, the leakage air enters the region bounded by the inner rails and the second and third portions, i.e., the legs, of the U-shaped supplemental seal. This leakage air forces those portions against the radially inner and outer surfaces of the inner band and nozzle support ring, respectively, thereby substantially preventing leakage flow into the hot gas path.
In another form of the present invention, generally arcuately extending supplemental seal sections having a sinuous shape in circumferential cross-section are provided and form an annular supplemental seal. Apices of the sinuous seal sections alternately engage against the radially inner and outer surfaces of the inner band and nozzle support ring, respectively. Anchor legs or first portions of these supplemental seal sections, as in the first embodiment, extend between the annular sealing surface of the nozzle support ring and the inner rails radially outwardly of the chordal hinge seals. To the extent any leakage past the chordal hinge seals pass the anchor legs of the supplemental seal sections, such leakage flow biases the apices of the sinuous seal sections into engagement with the sealing surfaces along the inner band and the nozzle support ring to substantially prevent any leakage flow past the chordal seals into the hot gas path.
In a preferred embodiment according to the present invention, there is provided a gas turbine comprising a turbine nozzle support ring having a generally axially facing first surface, a turbine nozzle segment having at least one stator vane and including an inner band having a second surface in axial opposition to the first surface, the support ring and a portion of the inner band of the segment defining a cavity generally radially outwardly of the first surface and in part defined by generally axially extending radially opposed surfaces of the support ring and the inner band and a flexible seal in the cavity including a seal body having a first portion extending between the first and second surfaces and second and third portions engageable with the radially opposed surfaces, respectively, to seal between high and low pressure regions on opposite sides of the axially registering first and second surfaces of the support ring and the inner band.
In a further preferred embodiment according to the present invention, there is provided a gas turbine comprising a turbine nozzle support ring having a generally axially facing annular first surface, a plurality of turbine nozzle segments each having at least one stator vane and including an inner band having a second surface, the second surfaces forming a second peripheral surface lying in axial opposition to the first annular surface, a first seal between the first and second surfaces for sealing between high and low pressure regions on opposite sides of the first seal and a secondary seal between the support ring and the nozzle segments on a side of the first seal exposed to the low pressure region for maintaining a seal between the high and low pressure regions upon leakage past the first seal.